Method for the measurement of lengths and angles and an equipment therefor

ABSTRACT

The invention relates to a method and to an arrangement for measuring length or angles, in which method use is made of a tape-shaped transmitter element (1) which is provided with markings and is designed to be pulled out of and pushed into a housing (6), easing or the like, the latter being provided with at least one sensor (4, 5) for detecting the markings on the transmitter element, and with an electronics unit (33) for converting signals from the sensor into length measurements or angle measurements. The sensor detects the markings on the transmitter element, which markings are in the form of embossings (2) in a repeated pattern of embossings, which form a micro-corrugated, ribbon-shaped zone (3) on the transmitter element, which micro-corrugated zone is moved past the sensor which registers and counts the number of elevations and/or depressions in the micro-corrugated zone, which elevations and/or depressions pass the sensor from a certain starting position to a certain measurement point, which is converted in the electronics unit to a measurement value of the length or angle in question.

TECHNICAL FIELD

The present invention relates to a method for measuring length orangles, in which method use is made of a tapeshaped transmitter elementwhich is provided with markings and is designed to be pulled out of andpushed into a housing, casing or the like, the latter being providedwith at least one sensor for detecting the markings on the transmitterelement, and with an electronics unit for converting signals from thesensor into length measurements or angle measurements. The inventionalso relates to equipment for carrying out the method.

PRIOR ART

It is generally known to use markings of a magnetic nature on thetransmitter unit of equipment of the abovementioned type. U.S. Pat. No.4,747,215 describes electronic measuring equipment which comprises ameasuring tape with a builtin magnetic strip on which magnetic markingshave been recorded, which markings can transmit signals to a sensor in atape housing. A measuring tape of this type has a number of particulardisadvantages. Among these may be mentioned the fact that the magneticstrip has to be embedded in the measuring tape so that the strip ismechanically protected. This is complicated and considerably increasesthe cost of the product. Nevertheless, there is still a risk of thestrip being damaged mechanically. Moreover, in all equipment based onpermanent magnetic markings, there is a risk that the markings will belost or will be altered as a result of demagnetization.

U.S. Pat. No. 4,316,081 is also based on permanent magnetic markings ina measuring tape. In this case the markings are in the form of magneticspheres arranged at a certain distance from one another. A disadvantageof this measuring equipment is that the degree of resolution isrelatively small. In addition, there is a risk of demagnetization inthis case too.

It is also known to use magnetoresistive conditions in order to measurelengths or positions. Examples of this technique are described in U.S.Pat. Nos. 4,712,064, 4,612,502, 4,039,936, 4,731,580, 4,053,829, in GB 2157 831 and in EP-B-0 164 832.

BRIEF DISCLOSURE OF THE INVENTION

An object of the invention is to offer a method and equipment of thetype specified in the preamble, which does not presuppose the use of anypermanent magnetic markings in the transmitter element. A particular aimof the invention is to offer equipment having a transmitter elementwhich is designed in such a way that it is adapted to magnetoresistivemeasurement, without markings of a permanent magnetic nature in thetransmitter element, which does not, however, preclude the possibilityof detection other than magnetoresistive detection being included withinthe scope of the invention. For example, laser detection or otheroptical detection of the markings on the transmitter element isconceivable.

A further aim of the invention is to offer a transmitter element whichcan be massproduced at very low cost and which, in combination withsuitable electronics, can nevertheless permit an extraordinarily highdegree of resolution and corresponding accuracy of measurement.

BRIEF DESCRIPTION OF THE FIGURES

In the following description of a preferred embodiment, reference willbe made to the attached drawings, in which

FIG. 1 is a perspective view of a part of a transmitter element in theform of a measuring tape,

FIG. 2 shows, schematically, the principle of the measuring technique,with a part of the tape being shown on a larger scale in a longitudinalsection through II--II in FIG. 1,

FIG. 3 shows, schematically, the main components of the equipment, and

FIG. 4 shows the electronic components of the equipment in the form of ablock diagram.

DESCRIPTION OF A PREFERRED EMBODIMENT

In FIGS. 1-3 a measuring tape is generally designated by thereference 1. It consists of coldrolled carbon steel, i.e. aferromagnetic, but not magnetized, material. The tape 1 has a widthwhich is normal for measuring tapes, i.e. about 15 mm, and a thicknessof about 0.12 mm. According to the embodiment, the tape has an S-shapedcross-section, which gives good flexural strength. Among other possibleforms, a conventionally curved form may be mentioned, and a completelyflat basic form of the tape 1 is also conceivable. It is also possibleto imagine the surfaces, which are situated on either side of thecentral zone, being provided with an embossed pattern which furtherimproves the flexural strength.

The feature particular to the invention is that the tape 1 has beenprovided with markings in the form of a repeated pattern of embossings 2which form a microcorrugated, ribbon-shaped zone 3 on the transmitterelement 1, which micro-corrugated zone 3 is intended to be moved past atleast one sensor (in the preferably chosen embodiment of the electronicsthere are two sensors 4, 5) in a tape housing 6 or the like duringmeasurement. An electronics unit has been designated by 33. According tothe embodiment, the transmitter element is in the form of a tape curvedin this case, which can apply in particular to equipment for anglemeasurement.

The embossings 2 in the zone 3 have a depth which, in the case of thetape thickness in question, is at least 0.05 and at most 1 mm. The depthof embossing is expediently of the same order of size as the tapethickness. As emerges most clearly from FIG. 1 and FIG. 2, theembossings 2 form regularly alternating elevations (peaks) anddepressions (valleys) in a continuous wave shape in the longitudinaldirection of the zone 3. The distinctive feature of this wave shape isthat it has regularly recurring maxima (peaks) and minima (valleys), andthat the inclination of the wave curve at all points between thesemaxima and minima forms an angle with respect to both the horizontaldirection and the vertical direction. For example, the embossed patterncan have the form of a sinusoid curve, or a curve which resembles asinusoid curve. The length of the wave V is, in the case of the tapethickness in question, at least 0.5 mm and at most 5 mm. A suitablelength of the wave is about 10 times the thickness of the tape, or about1 mm. The width of the zone 3 does not constitute a critical dimension,but it should be comparatively small so as not to affect seriously theflexural strength of the tape 1. A suitable zone width is 1-4 mm,expediently about 2 mm. The embossings 2 in the zone 3 are produced byrolling while the tape 1 is otherwise being given the desired profile.

Since the transmitter element is represented by a measuring tape 1, thedemands in respect of accuracy of measurement are generally moderate. Itsuffices in these cases to count, with the aid of the sensor or thesensors 4, 5, the number of embossings, or, more specifically, to recordthe number of maxima and minima in the curve pattern of the embossing 2,or, if appropriate, only the maxima (the peaks) or only the minima (thevalleys) which pass by the sensor/sensors when the tape is being movedinto or out of the tape housing 6. The sensor/sensors is/are preferablyof the magnetoresistive type. The impulses from the maxima and/or minimaare converted in the electronics unit to mm or inches, which are readoff on a liquid crystal digital display.

How the measurement proceeds for higher, or very high, demands inrespect of accuracy of measurement will now be explained in greaterdetail with reference also to FIG. 4, and at the same time theelectronics equipment will be described in greater detail. The basicprinciple of the measurement technique is that the signals from twodifferential magnetoresistive sensors 4, 5 are detected. These signals,which correspond to logged maxima and minima in the curve pattern of theembossing, are converted to pulses and counted. At positions between thesaid maxima and minima in the curve pattern, incremental or decrementalcalculation is also carried out by deter-mining the individualresistances of the sensor. The aggregate values are shown on a liquidcrystal digital display 8 in millimeters or inches.

In the block diagram shown in FIG. 4, references 9, 10 denote inputsfrom the differential sensor 4, while references 11, 12 denote inputsfrom the differential sensor 5. These inputs are connected to R/Iconverters 13-16, where the varying resistances of the respectivesensors are converted to current values. In pulse generators 17, 18,socalled comparators, the currents from the R/I converters are compared,and a high or low signal is emitted depending on which input is higherthan the other. The oscillators 19-22 are controlled from the R/Iconverters and give a frequency which is proportional to the inputcurrent. The actual frequency of each channel is calculated by a counter23-26 connected to the internal data bus 27. In addition, the counter isread off and reset to zero at regular intervals, this being carried outwith the aid of a crystal functioning at a frequency of 32 kHz in theunit 34. The time between two counted pulses is also calculated in acounter which is connected to the internal data bus. According to theembodiment, an oscillator functions with a crystal which emits 32 kHz. Avoltage control 29 controls the voltage to the units which have beendescribed.

The electronic equipment furthermore comprises a control unit 30, anarithmetic logic unit (ALU) 31 and a storage unit 32. How the variousunits are coupled can be seen from the block diagram in FIG. 4.Information relating to the form of the wave pattern in the embossedzone 3 is stored in the storage unit. Information is also availablerelating to the distance X between the two differential magnetoresistivesensors 4 and 5. This distance X is less than half the length of a waveV/2. In addition to the said maxima and minima of the resistance, whichcorrespond to maxima and minima in the wave pattern, measurements of thedistances D1 and D2, respectively, to the tape in the embossed zone 3are obtained in digital form. According to the program which has beenloaded, the incoming signals are treated incrementally or decrementallyin a digital manner, so that an adjustment value DL is obtained which isadded to the approximative measurement value Ln, which corresponds to acertain number n of half wave lengths, so that a measurement value Ln+DLcorresponding to a certain number of pulses is obtained which isconverted to millimeters or inches and can be read off on the digitaldisplay 8.

Despite the relatively large division between the teeth (the length ofthe wave) in the embossed pattern in the zone 3, it is possible toobtain a degree of resolution and a precision of measurement of theorder of 5-10 μm, which is made possible by the micro-corrugation andthe continuous wave form of the embossed pattern, in combination withthe magnetoresistive measurement technique.

I claim:
 1. In a method for measuring length which utilizes a measuringtape, at least one sensor, and an electronic unit housed in a casing,from which the tape can be pulled out of and pushed into or be displacedrelatively to it, comprising the steps of:a) forming the measuring tapefrom a ferromagnetic, but not magnetized, material, and b) forming onthe tape a ribbon-shaped zone with corrugations comprised of a repeatedpattern of embossings, including depressions and elevations, wherein theembossings depth is at least 0.05 mm, and wherein the repeated patternof embossings form a continuous wave shape in the longitudinal directionof the tape, c) passing the tape by said at least one sensor, the sensorbeing a magnetoresistive sensor adapted to magnetoresistive measurement,and d) providing the magnetoresistive measurements to the electronicunit to convert signals from the sensor into length measurements,whereby the sensor registers the numbers of depressions and elevationsin the ribbon-shaped corrugated zone.
 2. Method according to claim 1,wherein the tape is moved passed two differential magnetoresistivesensors, spaced apart from one another.
 3. Apparatus for measuringlength, comprising a measuring tape having two longitudinal, parallelside edges, a casing for the measuring tape which can be pulled out ofand pushed into the casing or be displaced relative thereto, markings onthe measuring tape, at least one sensor in the casing for detecting themarkings on the measuring tape, and an electronics unit in the casingfor converting signals from said sensor in to length measurements,whereina) the measuring tape has a thickness of at least 0.05 and atmost 1 mm; b) the body of the measuring tape, within a ribbon shapedzone of the measuring tape, said zone extending between and parallel toand at a distance from the side edges of the measuring tape, iscorrugated to form said markings consisting of a repeated pattern ofembossings, including depressions and elevations in the form oftransverse ridges and valleys on both sides of the measuring tape insaid ribbon-shaped zone; c) the measuring tape on both sides of saidribbon-shaped corrugated zone, between the ribbon-shaped corrugated zoneand the side edges of the measuring tape, has at least one zone which isvoid of corrugations having transverse ridges and valleys; d) theembossings have a depth of at least 0.05 mm; e) the repeated pattern ofembossings forming a continuous wave shape in the longitudinal directionof the ribbon-shaped corrugated zone, the length of the wave being atleast 0.5 mm; f) the measuring tape being at least substantially made ofa ferromagnetic, but not magnetized, material; g) and said at least onesensor is a magnetoresistive sensor provided to register the number ofat least one of said type of embossings as said embossings pass thesensor from a certain starting position to a certain measuring pointwhen the measuring tape is moved relative to the at least one sensor. 4.Apparatus according to claim 3, wherein the at least one sensorcomprises two differential magnetoresistive sensors that are arranged ata certain distance from each other along the ribbon-shaped corrugatedzone and wherein the electronics unit comprises a storage unit whichcontains information on the embossed pattern in the ribbon-shapedcorrugated zone and also information on the distance between thesensors.
 5. Apparatus according to claim 3, wherein the ribbon-shapedcorrugated zone has a width of between 1-4 mm.
 6. Apparatus according toclaim 3, wherein the embossing depth is at most 1 mm.
 7. Apparatusaccording to claim 3, wherein the wave length is at most 5 mm.